Interstitial lung diseases of unknown cause. Disorders characterized by chronic inflammation of the lower respiratory tract. (Second of two parts)
Diagnosis, staging, and therapy decisions concerning idiopathic pulmonary fibrosis, sarcoidosis, and histiocytosis X are made on the basis of combined information from the history, routine clinical assessment, chest x-ray films, physiologic testing, lung biopsy, bronchoalveolar lavage, and gallium-67 scanning. To diagnose these disorders accurately, a detailed history must be obtained that rules out the known causes of interstitial disease. Physical examination, chest x-ray films, and lung-function testing help, but for a definitive diagnosis it is necessary to combine these indexes with a morphologic assessment of the lung parenchyma. For sarcoidosis, transbronchial biopsy is the method of choice to obtain tissue. However, studies by Wall et al., have shown that for idiopathic pulmonary fibrosis and histiocytosis X, transbronchial-biopsy specimens are frequently inadequate and open biopsy is required. If a lung biopsy is not possible, bronchoalveolar lavage and gallium-67 scanning can help in the diagnosis, although neither method is definitive. For example, large proportions of neutrophils recovered by lavage suggest idiopathic pulmonary fibrosis, and large proportions of lymphocytes suggest sarcoidosis. However, there is sufficient overlap among the patterns of alveolitis associated with various interstitial, infectious, and malignant disorders that bronchoalveolar lavage should not be used alone as a major diagnostic criterion. The only exception is for histiocytosis X; an ultrastructural analysis that reveals histiocytosis X cells among those recovered by lavage strongly suggests this disease. Like lavage, gallium-67 scanning is generally nonspecific and cannot be used alone as a major diagnostic criterion. If there is clear evidence of diffuse interstitial disease, the uptake of gallium-67 by lymph nodes, the parotid gland, or other extrathoracic structures is strongly suggestive of sarcoidosis, but similar patterns can be seen in lymphoid tumors.